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Date: Sat, 29 Apr 2017 18:14:46 +0800
From: Baoquan He <bhe@...hat.com>
To: Kees Cook <keescook@...omium.org>
Cc: Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Dave Young <dyoung@...hat.com>, douly.fnst@...fujitsu.com,
Dan Williams <dan.j.williams@...el.com>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"x86@...nel.org" <x86@...nel.org>, Yinghai Lu <yinghai@...nel.org>,
Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v3 2/3] KASLR: Handle memory limit specified by memmap
and mem option
On 04/28/17 at 12:39pm, Kees Cook wrote:
> On Wed, Apr 26, 2017 at 3:16 AM, Baoquan He <bhe@...hat.com> wrote:
> > Option mem= will limit the max address a system can use and any memory
> > region above the limit will be removed.
> >
> > Furthermore, memmap=nn[KMG] which has no offset specified has the same
> > behaviour as mem=.
> >
> > KASLR needs to consider this when choosing the random position for
> > decompressing the kernel.
> >
> > This patch implements that.
> >
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > Acked-by: Kees Cook <keescook@...omium.org>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: x86@...nel.org
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Yinghai Lu <yinghai@...nel.org>
> > Cc: Borislav Petkov <bp@...e.de>
> > ---
> > arch/x86/boot/compressed/kaslr.c | 60 ++++++++++++++++++++++++++++++++--------
> > 1 file changed, 48 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > index 53a06ec..e5eb0c3 100644
> > --- a/arch/x86/boot/compressed/kaslr.c
> > +++ b/arch/x86/boot/compressed/kaslr.c
> > @@ -78,6 +78,10 @@ static bool memmap_too_large;
> > extern unsigned long get_cmd_line_ptr(void);
> >
> >
> > +/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
> > +unsigned long long mem_limit = ULLONG_MAX;
> > +
> > +
> > enum mem_avoid_index {
> > MEM_AVOID_ZO_RANGE = 0,
> > MEM_AVOID_INITRD,
> > @@ -128,16 +132,22 @@ parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
> > return -EINVAL;
> >
> > switch (*p) {
> > - case '@':
> > - /* Skip this region, usable */
> > - *start = 0;
> > - *size = 0;
> > - return 0;
> > case '#':
> > case '$':
> > case '!':
> > *start = memparse(p + 1, &p);
> > return 0;
> > + case '@':
> > + /* memmap=nn@ss specifies usable region, should be skipped */
> > + *size = 0;
>
> Please explicitly add a comment like /* Fall through. */ or something
> here, to help future reviewers. :)
Sure, will add. Thanks!
>
> > + default:
> > + /*
> > + * If w/o offset, only size specified, memmap=nn[KMG] has the
> > + * same behaviour as mem=nn[KMG]. It limits the max address
> > + * system can use. Region above the limit should be avoided.
> > + */
> > + *start = 0;
> > + return 0;
> > }
> >
> > return -EINVAL;
> > @@ -163,9 +173,14 @@ static void mem_avoid_memmap(char *str)
> > if (rc < 0)
> > break;
> > str = k;
> > - /* A usable region that should not be skipped */
> > - if (size == 0)
> > +
> > + if (start == 0) {
> > + /* Store the specified memory limit if size > 0 */
> > + if (size > 0)
> > + mem_limit = size;
> > +
> > continue;
> > + }
> >
> > mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
> > mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
> > @@ -189,6 +204,7 @@ static int handle_mem_memmap(void)
> > size_t len = strlen((char *)args);
> > char *tmp_cmdline;
> > char *param, *val;
> > + u64 mem_size;
> >
> > tmp_cmdline = malloc(COMMAND_LINE_SIZE);
> > if (!tmp_cmdline )
> > @@ -211,8 +227,20 @@ static int handle_mem_memmap(void)
> > return -1;
> > }
> >
> > - if (!strcmp(param, "memmap"))
> > + if (!strcmp(param, "memmap")) {
> > mem_avoid_memmap(val);
> > + } else if (!strcmp(param, "mem")) {
> > + char *p = val;
> > +
> > + if (!strcmp(p, "nopentium"))
> > + continue;
> > + mem_size = memparse(p, &p);
> > + if (mem_size == 0) {
> > + free(tmp_cmdline);
> > + return -EINVAL;
> > + }
> > + mem_limit = mem_size;
> > + }
> > }
> >
> > free(tmp_cmdline);
> > @@ -449,7 +477,8 @@ static void process_e820_entry(struct boot_e820_entry *entry,
> > {
> > struct mem_vector region, overlap;
> > struct slot_area slot_area;
> > - unsigned long start_orig;
> > + unsigned long start_orig, end;
> > + struct boot_e820_entry cur_entry;
> >
> > /* Skip non-RAM entries. */
> > if (entry->type != E820_TYPE_RAM)
> > @@ -463,8 +492,15 @@ static void process_e820_entry(struct boot_e820_entry *entry,
> > if (entry->addr + entry->size < minimum)
> > return;
> >
> > - region.start = entry->addr;
> > - region.size = entry->size;
> > + /* Ignore entries above memory limit */
> > + end = min(entry->size + entry->addr, mem_limit);
> > + if (entry->addr >= end)
> > + return;
> > + cur_entry.addr = entry->addr;
> > + cur_entry.size = end - entry->addr;
> > +
> > + region.start = cur_entry.addr;
> > + region.size = cur_entry.size;
> >
> > /* Give up if slot area array is full. */
> > while (slot_area_index < MAX_SLOT_AREA) {
> > @@ -478,7 +514,7 @@ static void process_e820_entry(struct boot_e820_entry *entry,
> > region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
> >
> > /* Did we raise the address above this e820 region? */
> > - if (region.start > entry->addr + entry->size)
> > + if (region.start > cur_entry.addr + cur_entry.size)
> > return;
> >
> > /* Reduce size by any delta from the original address. */
> > --
> > 2.5.5
> >
>
> Otherwise, this looks good to me.
>
> -Kees
>
> --
> Kees Cook
> Pixel Security
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